To quote yourself:
Jesus never mentioned anything (remotely specific) about the existence of exoplanets, smartphones, the Internet, Justin Bieber, telescopes, MRI scanners, NASA, the Arabic numeral system, etc. I could go on, but you get the point.
How is the undeniable existence of these things not mentioned by Christ any different from his lack of mention of spirits of people who die and hang around to be seen by us. Did Christ explicitly deny such a thing was possible any more than he denied things in my list above were possible?